Wafer production method

Abstract

A wafer production method for producing a wafer from an ingot oriented to have a c-axis inclined in an off-angle direction at an off-angle more than zero degree From a central axis includes steps of emitting a laser beam to a top surface that is one of end surfaces of the ingot opposed to each other in height direction thereof to form a separation layer at a depth from the top surface of the ingot which corresponds to a thickness of the wafer, applying a physical load in a single direction to a first end that is one of ends of the ingot which are opposed to each other in an off-angle direction to remove a wafer precursor from the ingot at the separation layer, and planarizing a major surface of a removed object derived by separating the wafer precursor from the ingot at the separation layer, thereby forming a wafer. The ingot has a given degree of transmittance to the laser beam. The wafer precursor is created by a portion of the ingot between the top surface of the ingot and the separation layer.

What is claimed is: 
     
         1 . A wafer production method for separating a wafer from an ingot which is made from single-crystal SiC and has a c-axis and a C-surface which extend perpendicular to each other, comprising:
 a separation layer formation step of emitting a laser beam to a top surface that is one of end surfaces of the ingot opposed to each other in height direction of the ingot to form a separation layer at a depth from the top surface of the ingot which corresponds to a thickness of the wafer, the ingot having a given degree of transmittance to the laser beam;   a wafer separation step of separating a wafer precursor from the ingot at the separation layer, the wafer precursor being created by a portion of the ingot between the top surface and the separation layer;   a wafer flattening step of flattening a major surface of a plate-like removed object derived in the wafer separation step, wherein   the c-axis of the ingot is oriented to be inclined in an off-angle direction at an off-angle from a central axis which is defined to extend perpendicular to the top surface, the off-angle being greater than zero degrees, and   separation of the wafer precursor from the ingot is achieved by applying a physical load in a single direction to a first end that is one of ends of the ingot which are opposed to each other in the off-angle direction.   
     
     
         2 . The wafer production method as set forth in  claim 1 , wherein the first end of the ingot is located on a high-level side of the ingot when the ingot is oriented to have the top surface facing upward. 
     
     
         3 . The wafer production method as set forth in  claim 1 , wherein formation of the separation layer is achieved with a facet area of the ingot located at a low height side of the C-surface when the ingot is oriented to have the top surface facing upward. 
     
     
         4 . The wafer production method as set forth in  claim 1 , wherein the separation of the wafer precursor is achieved by applying the physical load to an area of the ingot which does not overlap the facet area in a circumferential direction around the central axis where the top surface of the ingot defines a Si-surface thereof, the ingot is oriented to have the top surface facing upward, and the facet area is located at a high height side of the C-surface. 
     
     
         5 . The wafer production method as set forth in  claim 1 , wherein the separation layer formation step is to perform a laser scanning operation a plurality of times in which the laser beam is emitted to the top surface and swept to move a laser exposure position where a portion of the top surface is exposed to the laser beam in a first direction along the top surface,
 the separation layer forming step steers the laser beam in a second direction which is oriented perpendicular to the first direction along the top surface in each of the laser scanning operations, thereby developing a plurality of scan lines which are defined by laser notches and each of which extends in the first direction to form the separation layer, the scan lines being arranged adjacent each other in the second direction,   each of the scan lines is created by sweeping the laser beam to move the laser exposure position in the first direction so that each of the scan lines extends in an entire region between ends of the top surface which are opposed to each other in the first direction,   the laser scanning operations include a return laser scanning operation which sweeps the laser beam to move the laser exposure position in a direction opposite the first direction to create at least one of the laser notches in at least one of ends of the top surface which are opposed to each other in the first direction.   
     
     
         6 . The wafer production method as set forth in  claim 1 , wherein the separation of the wafer precursor is performed by continuously or intermittently raising a level of the load exerted on the ingot. 
     
     
         7 . The wafer production method as set forth in  claim 1 , wherein the wafer separation step includes;
 joining the top surface of the ingot and a top surface-retaining member together;   joining a bottom surface that is an end surface of the ingot opposed to the top surface in a height direction of the ingot to a bottom surface-retaining member; and   applying the load to the top surface-retaining member and/or the bottom surface-retaining member, wherein   each of the joining of the top surface and the top surface-retaining member and the joining of the bottom surface and the bottom surface-retaining member is achieved by placing adhesive inside an outer periphery of the ingot and then spreading the adhesive using thermal energy and/or mechanical pressure.   
     
     
         8 . The wafer production method as set forth in  claim 7 , wherein in each of the joining of the top surface and the top surface-retaining member and the joining of the bottom surface and the bottom surface-retaining member, the adhesive is spread outside a side surface of the ingot which extends between the top surface and the bottom surface of the ingot until the adhesive sticks to the side surface. 
     
     
         9 . The wafer production method as set forth in  claim 1 , wherein the separation of the wafer precursor is achieved by applying both static pressure and dynamic pressure to the ingot.